Mass Extinctions

What’s a mass extinction? a sharp decrease in the number of species in a relatively short period of time. There are different ways a mass extinction can occur including… Asteroids Comets Global warming Ice age And more…

How many mass extinctions have there been? http://www.inexistentia.net/nuke.jpg

5

The Ordovician-Silurian Extinction

439 million years ago Caused by a drop in sea level as glaciers formed, then by rising sea levels as glaciers melted. Killed about 25% of marine families Killed 60% of marine genera

Late Devonian extinction

About 364 million years ago About 22% of marine families were killed About 57% of the genera were killed Suggested that a asteroid impact was the prime cause

Permian-Triassic extinction

Most likely due to volcanic eruption, an asteroid impact or a nearby supernova

Informally called the “Great Dying” Occurred about 251 million years ago It was the most severe extinction 96% of all marine species were killed 70% of terrestrial vertebrate were killed the extinction took a few million years Normal levels of biodiversity did not become present until 6 million years after the end of the Permian

End Triassic extinction

199 million to 214 million years ago caused by massive floods or lava erupting from central Atlantic province – an event that triggered the opening of the Atlantic Ocean The volcanism may have lead to deadly global warming 22% of Marine families 52% of marine genera Vertebrate deaths unknown

Cretaceous-Tertiary extinction

No one knows exactly how this Mass Extinction happened and why it happened at such a rapid rate.

The first and the most favored theory is that an asteroid hit somewhere in the golf of Mexico in the Yucatan Peninsula 65 million years ago. The Asteroid impact is site is called the Chixclub and is approximately 200 Kilometers across making the asteroid itself about 9 miles wide

caused Forest fires to start and ignited volcanic eruptions all over the glob as well as tidal waves, severe storms that would eliminated all sunlight. It would be six months before sunlight would reach the ground after such a blow. The dinosaurs, even in their prime, stood no chance without sunlight and plant life, ending the dinosaurs 165 million year reign.

One of the other theories is that climate change killed all of the plant eating dinosaurs due to lack of food from the climate change. The cretaceous period was tropical and so were almost 50 percent of the plants. If the temperature was to change drastically the plant eater’s food would slowly dwindle. With the plant eaters becoming extinct the carnivores would soon run out of food as well.

Volcanic eruptions have also been theorized to have killed of the dinosaurs. When volcanoes erupt they send clouds of dust, sulfuric acid, and poisonous gas that would have made it impossible to breath. This would result in the blocking of sunlight and a severe climate change. This would have been nearly impossible to survive in this environment

Which do you think killed the dinosaurs????

The Big Five Ordovician-Silurian extinction - 439 million years ago, Late Devonian extinction - 364 million years ago Permian-Triassic extinction - 251 million years ago End Triassic extinction, - 199 million to 214 million years ago Cretaceous-Tertiary extinction, about 65 million years ago

The sixth mass extinction? This extinction is referred to as the Holocene extinction. This is named after what geologists call the period we as humans have been in. The immense amount of extinction during this period of plants and mammals has constituted is as a mass extinction to many scientists. The extinctions include birds, mammals, reptiles, and amphibians.

This extinction is thought to have started once Homo sapiens started dispersing outward from Africa on the land bridges, hunting and gathering was the start of the extinctions induced by man. Today approximately 1,000 species out of the worlds 10,000 are on the verge of extinction. There is no conclusive evidence but it is estimated that since Homo sapiens began hunting and gathering some 500,000 – 1,000,000 species have become extinct, from over hunting, population, and most importantly pollution.

What do you think, are we in the midst of a mass extinction???